I think they always just use 1.00 but I am not sure
252 Atk Urshifu Wicked Blow vs. 252 HP / 0 Def Abomasnow on a critical hit: 130-154 (65.9 - 78.1%) -- guaranteed 2HKO
This is a calculation with a guaranteed critical hit. As you can see, this has a variance in the percentages (65.9 - 78.1%). This means that yes, it does vary.